It is known to provide prestressed pressure vessels of cast material, e.g. cast iron or steel, as pressure vessels for nuclear-reactor installations and particularly for housing the high-temperature reactor core.
In such systems it is also a common practice to provide a number of heat-exchange components and horizontal gas passages which communicate between the heat exchangers and the reactor vessel for connecting the high-temperature reactor with the primary coolant flow.
In such systems, the pressure vessel for the high-temperature reactor can be centrally located and the centrally disposed reactor vessel can be surround by a plurality of pressure vessels each containing heat-exchanger or other components. These auxiliary vessels may also be provided as separate prestressed pressure vessels of cast material. The component vessels can be disposed in a partial circle around the central or reactor vessel, i.e. can be annularly spaced therearound.
Prior to the development of such systems, efforts in this field concentrated upon the provision of a completely integrated reactor assembly in which the high-temperature reactor and the primary coolant components, such as tube furnaces or steam generators (more generally referred to as heat exchangers) were provided in a common prestressed concrete pressure vessel.
When, however, attempts are made to construct similar vessels from cast materials such as cast iron or cast steel (more generally cast metals) problems were encountered not only because of the large quantities of materials which were required and their expense, but also because the fabrication time was realtively great and it was difficult, even with existing casting technology, to fabricate such vessels.
This is especially the case because nuclear-reactor installations with their primary coolant components are extremely large and the tendency toward the fabrication of still larger units is increasing. The fabrication of a single pressure vessel for such systems has thus become not only difficult but also uneconomical.
As a result, it has been proposed to substitute for this single housing for the integrated system, an arrangement in which the high-temperature reactor and the primary coolant components are contained in separate pressure vessels in a satellite construction wherein the component vessels are disposed around a central reactor vessel.
In this case, the pressure vessels for the primary coolant components are disposed in a partial circle around the reactor pressure vessel. Two horizontal gas conduits generally connect each of the component vessels with the high-temeprature reactor vessel for the delivery of the gas to the component vessel and return of the primary coolant to the reactor, respectively.
These gas conduits required a correspondingly large number of passages in the cylinder walls of the prestressed pressure vessels which detrimentally effected the strength of both the reactor vessel and the component vessel. Naturally, attempts were made to overcome this weakening of the reactor vessel by reinforcement, although this increases the cost and amount of material which must be used.
In the German patent publication (open application or Offenlegungsschrift) No. 23 26 917, there is described a nuclear-reactor installation in which the nuclear reactor is contained in a high-pressure vessel which is, in turn, surrounded by a cylindrical concrete containment or structure. Two heat exchangers are, in this system, connected with the reactor pressure vessel by coaxial ducts and are received, in turn, with respective burst-resisting containments reinforced by steel reinforcing cables or the like and composed of concrete. The containments are each applied to a concrete cylinder and the two concrete cylinders form part of the cylindrical concrete housing and are adapted to receive the drive motors for the primary coolant circulating pumps.
It is also known in this art to provide a reinforced concrete pressure vessel for nuclear reactors in which the desired or required volume is subdivided between two or more vessels each of which can be prestressed and all of which can be collectively surrounded by further prestressing cables into a unit.
In this construction, represented by the German Patent document (open application or Offenlegungsschrift) 16 84 594, the central vessel is larger than the peripheral vessels and serves to receive the nuclear reactor while four smaller vessels grouped around the central vessel receive the primary coolant components such as heat exchangers and coolant circulation components. The central vessel and the outer vessels are provided with horizontal passages so that the central vessel is connected with each of the outer vessels by two gas conduits.
In still another prior-art proposal, the pressure vessel for the high-temperature reactor is connected with the pressure vessels for the steam-generating components by burst-resisting connecting passages disposed beneath these pressure vessels. In this fashion the weakening of the cylindrical wall portions of the pressure vessels is avoided but the cost is increased since the passages must be sufficiently prestressed and strengthened in a redundant manner.